Briefly introduce the processing technology of M1M2 self-locking tuning screw.
Processing Technology Analysis of M1M2 Self-locking Tuning Screw
As a miniature precision fastener, M1M2 self-locking tuning screw is widely used in the fields of electronic communication, precision instruments, radio frequency equipment, etc. Its processing technology needs to give consideration to miniature size accuracy, reliability of self-locking function and thread adaptability. The core is four links: "raw material pretreatment-precision forming-self-locking structure processing-precision detection". The specific process is as follows:
First, raw material selection and pretreatment
Selection of raw materials: High-strength stainless steel (such as 304 and 316), phosphor bronze or titanium alloy are preferred, which should meet the requirements of toughness and wear resistance of micro-machining. The diameter of raw materials is selected according to the size of the finished screw shaft (usually φ1.0-2.0mm wire) to ensure uniform machining allowance (0.1-0.2mm).
Pretreatment process: the wire is straightened (straightness ≤0.01mm/m) to remove the scale and oil stain on the surface (by pickling, phosphating or ultrasonic cleaning); For stainless steel, annealing treatment (temperature 800-900℃, heat preservation for 1-2 hours) is needed to reduce hardness (HRC≤25), improve processing plasticity and avoid cracking in subsequent molding.
Second, precision molding processing
Cold heading forming: using multi-station micro cold heading machine, the screw head (such as cross groove, hexagon socket and round head) is gradually stamped and formed through the die. During cold heading, the pressure (5-10MPa) and die precision (dimensional tolerance ±0.005mm) are controlled to ensure that the coaxiality between the head and the rod is ≤0.01mm, and the height and diameter of the head meet the design requirements without burr and flash.
Finishing/grinding of the rod: the rod after cold heading is precisely machined, and the diameter tolerance of the rod is controlled (±0.003mm) by using a micro CNC lathe or a centerless grinder to ensure that the surface roughness Ra is less than or equal to 0.8 μ m; For long rod screws (length > 5 mm), it is necessary to ensure that the straightness of the rod is ≤0.005mm to avoid sticking during assembly.
Three, thread and self-locking structure processing (core process)
Precision thread processing: thread rolling machine is used for thread rolling (compared with thread turning, the strength is higher and the accuracy is more stable), the thread specification conforms to M1/M2 standard (pitch is 0.25mm/0.4mm), and the tolerance of thread pitch is controlled at 6H/6g level; Before thread rolling, it is necessary to finely calibrate the thread rolling wheel, and control the pressure and speed during the rolling process to ensure that the thread is free from tooth disorder and tooth collapse, and the tooth profile is full.
Processing of self-locking structure: select the corresponding process according to the self-locking requirements;
Friction-type self-locking: rolling tiny tooth lines (tooth height is 0.01-0.03mm) or coating wear-resistant coating (such as PTFE and titanium nitride) on the thread surface to enhance the friction during thread engagement and prevent loosening;
Interference self-locking: micro interference (0.002-0.005mm) is generated in the thread profile by precise rolling, and elastic interference is formed during assembly to realize self-locking;
Nylon locking ring type: For M2 screws, a nylon ring (made of PA66) is injected under the head. When the nylon ring engages with the nut, it will be extruded and deformed to provide self-locking force (a micro injection mold is required).
Fourth, heat treatment and surface treatment
Heat treatment: after forming, quenching and tempering are carried out, the quenching temperature of stainless steel is 1050-1100℃, and the tempering temperature is 400-500℃, so as to ensure that the hardness reaches HRC35-45 and improve the strength and wear resistance of screws; Screws for precision instruments can be tempered at low temperature (200-300℃) to reduce deformation.
Surface treatment: choose the treatment method according to the use environment;
Rust prevention requirements: zinc plating (blue-white zinc, colored zinc) and nickel plating, with the coating thickness of 5-10μm, to ensure that the salt spray test is ≥ 48h;
Precision conductive requirements: silver plating and gold plating, with a coating thickness of 1-3μm to ensure conductive performance and contact reliability;
High temperature environment: Passivation treatment is adopted to form a dense oxide film to improve high temperature resistance and corrosion resistance.
Five, precision detection and screening
Dimensional accuracy detection: key parameters such as head size, rod diameter, thread pitch, etc. shall be detected by tool microscope and secondary imager, and the tolerance shall conform to GB/T 196-2003 thread standard; Use a coaxiality tester to detect the coaxiality between the head and the rod to ensure that it is ≤ 0.01 mm..
Self-locking performance test: The locking torque and loosening torque are detected by a torque tester to ensure that the locking torque meets the design requirements (usually 0.5-2 nm), the loosening torque is ≥ 80% of the locking torque, and there is no automatic loosening phenomenon.
Appearance and defect screening: using automatic visual inspection equipment to check the defects such as thread burr, head crack and surface scratch; Internal hidden cracks are detected by magnetic particle flaw detection to ensure that the qualified rate of finished products is ≥99.5%.
VI. Packaging and Storage
After cleaning and drying, the finished product shall be packaged separately with anti-static packaging bags or sealed boxes to avoid wear or corrosion during transportation; The storage environment should be dry and ventilated (relative humidity ≤60%) to avoid high temperature and corrosive gas and ensure the stability of screw performance.
To sum up, the core of the processing technology of M1M2 self-locking tuning screw lies in "micro-precision molding" and "precise control of self-locking structure". It is necessary to ensure the dimensional accuracy, self-locking reliability and use stability of the product through high-precision equipment, strict process parameter control and whole-process detection to meet the assembly requirements of micro-precision equipment.
